The present invention relates to improvements in motion transmitting apparatus in general, and more particularly to improvements in apparatus wherein rotary movements of a first part initiate axial and/or other movements of a second part and/or of the first part.
Motion transmitting apparatus of the type to which the present invention pertains include so-called axial drives or axial transmissions, also called spindle drives, wherein an externally threaded rotary shaft-like member spindle or feed screw mates with an internally threaded part so that rotation of the spindle relative to the internally threaded part results in axial movement of the internally threaded part and/or vice versa. The externally threaded part can be rotated by a suitable prime mover (e.g., by an electric motor) or by hand. Spindle drives of the just outlined character are utilized, for example, in so-called screw presses.
The extent of axial movement of the externally threaded part relative to the internally threaded part of a standard spindle drive depends upon the lead or pitch of the mating internal and external threads as well as upon the number of revolutions of the driven part. Furthermore, the pitch or lead of the mating threads determines the ratio of the spindle drive, namely the extent of axial movement of the internally threaded part or the externally threaded part per revolution.
Conventional spindle drives can also serve to effect radial movements of one of the cooperating parts relative to the other part, e.g., of the internally threaded part relative to the externally threaded part. Furthermore, motion transmitting apparatus employing mating internal and external threads can be utilized to effect radial displacements of the two mating parts; drives of such nature are known as chucks or collets and can serve to maintain certain devices in predetermined fixed positions.
It has been found that the ratio of conventional spindle drives, chucks, collets and analogous apparatus (i.e., a ratio which depends upon the lead or pitch of the mating threads and/or upon the root diameter of the external thread) is often too small, even if the means for rotating one of the mating parts includes a rapidly rotating electric motor or an analogous prime mover. This holds true irrespective of the output of the prime mover (such as an electric motor) which supplies torque for rotation of one of the mating parts.
Another drawback of conventional drives or apparatus of the above outlined character is their relatively high cost, not only the initial cost (which includes the cutting or rolling of internal and external threads) but also the maintenance cost. Thus, in the absence of repeated and intensive lubrication, a conventional spindle drive is bound to require increased quantities of energy due to increased friction between the mating internal and external threads.